1. Field of the Invention
The present invention relates to a tunnel excavator for tunneling into the ground, such as in coal mines.
2. Description of the Related Art
Tunnel excavators used in excavating ground such as in coal mines include those comprising a forward body which is provided with a cutter for excavating the ground and rear body connected to the forward body by a propulsion jack. Such tunnel excavators bore into the ground as they move like inchworms, expanding and contracting the propulsion jack while a rear gripper established on the rear body and front gripper established on the forward body alternately push against and are separated from the tunnel.
Specifically, the propulsion jack is extended with the front gripper separated from the tunnel while the rear gripper is pressed against the tunnel and the front body moves forward relative to the rear body. Next, once the propulsion jack has extended by the prescribed stroke length, the propulsion jack is contracted with the rear gripper separated from the tunnel while the front gripper is pressed against the tunnel and the rear body is drawn forward to the forward body.
With this tunnel excavator, the propulsion reaction force of the propulsion jack is borne by the tunnel through the front gripper or rear gripper. In areas having faults, therefore, the propulsion reaction force is not attained from the grippers because the ground is broken up and it becomes impossible to tunnel forward. In areas where the ground is not strong, tunneling becomes impossible because the tunnel (walls) is destroyed by the pressure of the grippers. Backwards movement of the excavator is also difficult.
On the other hand, there are tunnel excavators which move forwards on crawlers instead of using grippers. This type of tunnel excavator is often difficult to operate because lateral sliding or the like occurs in areas where the coefficient of friction of the tunnel floor in contact with the crawlers is different on each side of the crawlers. Such tunnel excavators do not have a bearing frame to support the earth (i.e., roof and ribs of the tunnel). In the event of a fall, the various instruments constituting the excavator are damaged.